The object of this grant is to understand how the cellular architecture, in particular the actin cytoskeleton, influences embryonic development. Embryonic development is characterized by the formation of body axes (e.g., antero-posterior or a-p) and the differentiation of blastomeres that give rise to major tissues. The actin cytoskeleton is known to play a major role in these processes. We have identified an actin binding protein (ABP), CABP11, that promises to provide significant insights into actin-mediated events that occur during embryogenesis since: 1). CABP11 is a new ABP; 2). CABP11 is asymmetrically targeted to the anterior of 1 -cell embryos; to our knowledge, this is-only the second known ABP that behaves this way; 3). Reduction of CABP11 from embryos results loss of blastomere identity, loss of a-p axis asymmetry, and loss of membrane integrity around cells; 4). CABP11 appears to bind actin directly and associate with membranes. CABP11 is therefore at the intersection of the vital processes of embryonic development and regulation of the plasma membrane/actin cortex. This grant makes use of genetic experiments to decipher the function of CABP11 in embryonic cells. CABP11 protein will be removed from early embryos and the response of known signal transduction and polarity pathways will be assessed. This grant also makes use of cell biology experiments to ascertain the cellular requirements for CABP11 asymmetric localization and the mechanism by which this happens by studying movements of the protein in live embryos. Finally, this grant uses biochemistry to study the physical interactions between CABP11 and membranes, actin, and other proteins important for its function. In this way a unique and detailed mosaic of how the actin cytoskeleton functions in development will be put together. The issues central to this grant are of significant biological importance vis-a-vis cell identity, signal transduction, control of cell polarity, and potentially cell motility and wound healing.